1. Field of the Invention
The present invention relates to a capillary column used in gas chromatography.
2. Description of the Related Art
A capillary column for gas chromatography generally has a circular-shaped cross section, and it is theoretically known that when the length of a column is the same, higher resolution can be obtained by narrowing the inside diameter of the column. For example, a capillary column having a circular-shaped cross section (hereinafter abbreviated as “circular capillary column”) having the minimum diameter among the circular capillary columns available at present has an inside diameter of 0.1 mm, has a high theoretical plate number of 9000 plates/m (p/m), and can obtain high resolution. However, a problem of a circular capillary column having an inside diameter of 0.1 mm is that sufficient sample load capacity cannot be obtained.
Note that, in the present application, the “sample load capacity” of a certain capillary column means the maximum sample capacity at which peaks of sharp identical shape can be obtained when the capillary column is used in gas chromatography. That is, as the sample load capacity becomes larger, gas chromatography can be performed without diluting or dividing a sample, and thereby the detection sensitivity of minor components is also advantageously improved. Here, the “sample load capacity” of a certain capillary column is represented by the ratio to the sample load capacity of a circular capillary column having an inside diameter corresponding to the maximum width of the inside dimension in the thickness direction of the capillary column.
On the other hand, in contrast to the circular capillary column, a theory is proposed that a higher resolution than that of the circular capillary column can be obtained by changing the shape of the cross section to a rectangular shape (refer to H. D. Papendick et al., J. Chromatogr., 122, 443-450 (1978)). Here, if the inner peripheral length of the rectangular cross section is the same as the inner peripheral length of the circular capillary column, a capillary column having a rectangular cross section will be able to obtain higher sample load capacity as compared with the circular capillary column and thus have both high resolution and high sample load capacity.
However, the above theory has only showed the superiority of the capillary column having a rectangular cross section over the circular capillary column by a mathematical expression and the capillary column having a rectangular cross section has not been realized.
On the other hand, a capillary column having a rectangular cross section has also been proposed (for example, refer to Japanese Patent Laid-Open No. 2006-177917). The above conventional capillary column having a rectangular cross section is prepared by opposing two partition walls each made of a stainless steel sheet having a thickness of 0.2 mm and a width of 100 mm, disposing stainless steel sheets each having a thickness of 0.2 mm and a width of 5 mm at both ends of the partition walls as a spacer, brazing the spacers to the partition walls, and applying a material serving as a stationary phase to an inner surface of the capillary column. Alternatively, the capillary column may be prepared by applying the material serving as a stationary phase to the inner surface of the partition walls and then bonding or soldering both ends of the two opposed partition walls.
However, it is difficult to produce the capillary column having a rectangular cross section as a long capillary column up to tens of meters, and there is an inconvenience that even if the capillary column can be produced, it is difficult to form the stationary phase uniformly because the boundary of the partition wall and the spacer on the inner surface of the capillary column is right-angled.